Silver halide emulsion fogged with a boron hydride and a gold compound

ABSTRACT

DIRECT-POSITIVE PHOTOGRAPHIC ELEMENTS OF HIGH SPEED AND MAXIMUM DENSITY ARE PREPARED BY INCORPORATING IN THE SILVER HALIDE EMULSION AT LEAST ONE BORON HYDRIDE CONTAINING FROM 6 TO 12 BORON ATOMS IN WHICH THE SKELETAL FRAMEWORK FORMS A POLYHEDRON OR A FRAGMENT THEREOF, AND WHICH MAY CONTAIN HETEROSKELETAL ATOMS SELECTED FROM THE GROUP CONSISTING OF CARBON, SULFUR AND NITROGEN, AND A GOLD COMPOUND.

United States Patent 3,752,674 SILVER HALIDE EMULSION FOGGED WITH A BORON HYDRIDE AND A GOLD COMPOUND William Arthur Pritchett, Jr., Rochester, N.Y., assignor to E. Lldu Pout de Nemours and Company, Wilmington De NoDrawing. Filed June 22, 1971, Ser. No. 155,629 Int. Cl. G03c 1/28 US. Cl. 96-108 12 Claims ABSTRACT OF THE DISCLOSURE Direct-positive photographic elements of high speed and maximum density are prepared by incorporating in the silver halide emulsion at least one boron hydride containing from 6 to 12 boron atoms in which the skeletal framework forms a polyhedron or a fragment thereof, and which may contain heteroskeletal atoms selected from the group consisting of carbon, sulfur and nitrogen, and a gold compound.

BACKGROUND OF THE INVENTION This invention relates to direct-positive colloid-silver halide emulsions. Most particularly it relates to such emulsions which are prefogged by a synergistic combination of chemical fogging agents.

PRIOR ART Direct-positive emulsions are, of course, well known and there are many different methods of producing direct positive images. For example, a silver halide emulsion may be given a short overall exposure of high intensity radiation and then given a longer imagewise exposure of lower intensity. Upon development, a direct positive image will be obtained. Another method is to expose imagewise and develop and bleach-out developed silver and then flash expose and redevelop. A still further method is to use emulsion coated elements which have been chemically fogged with, for example, formaldehyde, hydrazine, sodium arsenite, silver ions and other fogging agents such as gold salts and sulfur compounds. Combinations of the above compounds such as hydrazine and gold salts have also been suggested. Upon imagewise eX-- posure and development of such chemically fogged elements, a positive image is obtained directly. In direct positive photographic elements utilizing this latter method, there is usually incorporated a desensitizing compound, usually a colored desensitizing dye.

The prior systems have some shortcomings in terms of speed, contrast and other sensitometric characteristics. When using a sufiicient quantity of reducing agent, e.g., stannous chloride, the fogged siliver halide grains cannot be easily bleached so that excessively long exposure is required and clean backgrounds or low minimum densities cannot be obtained. When gold compounds are used alone, difiiculties'are again experienced in obtaining sufiicieutly fogged grains and, as in the case of stannous chloride, the fogged grains are not easily bleached without impractically long exposures. It has been proposed to increase the speed of the above systems by adding certain dyes but, in many cases, this causes undesirable stain. A significant improvement resulted from the use of amine boranes as chemical fogging agents in direct positive emulsion systems. Direct positive emulsions and elements comprising such'emulsions are described and claimed in U.S. patents Bigelow and Burt, 3,361,564, Ian. 2, 1968 and Burt, 3,445,235, May 10, 1969. Overman 3,655,390, Apr. 11, 1972 and Burt 3,607,288, Sept. 21, 1971. US. 3,445,235 discloses and claims the use of rhodium and iridium salts in the direct positive emulsions of Bigelow et a1. 3,361,564 and the Overman patent discloses the use of bismuth as antikinki ng agents. US. 3,607,288 discloses the use of gold salts in direct positive emulsions chemically fogged with amine boranes to reduce the tendency for red light to bleach the fogged layer. Further improvements were made in shelf life or aging stability and contrast of direct positive elements by use of boron hydrides in which a skeletal framework forms a polyhedron or fragment thereof, and which may contain heteroskeletal atoms selected from the group consisting of carbon, sulfur and nitrogen. The compounds are added in quantities ranging up to 2.4X10' mole per 1.5 moles of silver under pH conditions of 3.0 to 9.0. Direct positive elements comprising such emulsions are described and claimed in assignees Bigelow, US. Patent 3,637,392, Jan. 25, 1972. Compared to a typical commercial film of the prior art which are chemically fogged with e.g., formaldehyde, the speed, of which, in terms of /EX10- is about 109, the direct positive elements containing the borane compound have speeds ranging from 126 to 14,000.

SUMMARY OF THE INVENTION It has now been found that improved high quality direct positive silver halide emulsions, speed and contrast can be obtained by the use of a synergistic combination of (1) at least one boron hydride in which the skeletal framework forms a polyhedron or fragment thereof containing from 6 to 12 boron atoms and may contain heteroskeletal atoms selected from the group consisting of carbon, sulfur and nitrogen atoms and (2) a gold compound. The boron hydride or cyclic boranes may be added in the range of 10 to 10- mole per mole of silver and the gold compound which may be a watersoluble salt or an acid such as hydrochloroauric acid may be added in the range of 1.0- to 10 mole per mole of silver nitrate. 'Ihe synergistic combination of borane and gold compounds may be added to the emulsion at a pH9.0. The borane compounds may be added as a solution with a suitable solvent, i.e., Water, ethyl alcohol, benzene, acetone, dioxane, etc. The useful borane compounds in aqueous solutions have greater stability than the amine boranes of the above Bigelow and The effectiveness of some borane compounds of Bigelow, US. Pat. 3, 637,392 in fogging a silver halide emulsion is not affected by the pH of the systems and they show good fogging properties under acid as well as alkaline conditions. Certain borane compounds are more effective than others when used in equivalent quantities. According to this invention it is important that the borane and gold compounds be added at the beginning, during or before the end of the digestion period after the excess salts have been removed by washing. The pH of the system can be adjusted to 9.0 or below and preferably is adjusted to 7.0 or below. The fogging effect produced by the borane compound/gold ion combination is bleachable by light prior to development. The emulsions of the invention may also contain rhodium or iridium in an amount of 1.5 to 325 mg. of a salt of such elements per mole of silver. Suitable salts are described in {U.S. Pat. 3,445,235.

Suitable developers are conventional, alkaline, photographic developing solutions useful for standard direct positive emulsions in the absence of the novel fogging combination. While the silver halide system used in this invention is generally a silver chlorobromide, other types, e.g., silver chloride, silver iodobromide, silver iodochloride and silver iodobromochloride, may be used with the boron hydride/gold compound combination.

useful in the fogging composition of this invention are the homonuclear boranes, polyheteronuclear boranes comprising polyhedral azoboranes, polyhedral thiaboranes and In evaluating the processed strips, the maximum density is the highest density on the step wedge. The speed of a typical low speed commercial direct positive in terms of 100/E 10- is 10-3 and the conventional material has a polyhedral carboranes, representative examples of which D of about 3.5. areshown in the following list. The invention will now be illustrated in and by the following examples:

COMPOUND EXAMPLE 1 4)2 1o 10 A direct positive emulsion was made in the following B m manner. To acidified aqueous solutions of gelatin each 3)a 9 12 containing 1 mole of KCl and 6.8x 10 mole of RhCl3', 3)4 a)2 9 1z there were rapidly added solutions containing 1 mole of s 5)a a ]2 u 11 AgNO To each of the resulting mixtures there was added m m s 0.4 mole of KBr in aqueous solution and the emulsions 3)4 3)3 10 12 were then ripened by heating for 10 minutes at 160 F. A (CH NHB H CH second quantity of 0.6 mole of KBr in aqueous solution B H- [S(CH3)2]z was added to each and the emulsions were again ripened B H S(C H for 10- minutes at 160 F. B H [S(C H5)2h The resulting silver bromochloride emulsions were C H B H S then coagulated, washed and redispersed in the manner Na B H lH O disclosed in Moede, U.S. Patent 2,772,162, Nov. 27, 1956. B C H The temperature of the redispersed emulsion was raised Cs(CH NB H to 130 F. and there was added an aqueous solution con- Cs B H taining 6.1% gelatin. The pH was adjusted to 5.5 using CSB 'H CI-I 0.6 M NaOH. The borane compound, CsB H S was added to each emulsion as shown in the table below and then a Methods of preparatwn of these compounds may be solution of hydrochloroauric acid (HAuCl was added found in The Chemistry of Boron and Its CQmPOImdS, in quantities shown in the tables and then the emulsion Meutterties, John Wiley and $0115, N'Y'! 1967; ywas digested at 130 F. for 40 minutes. The emulsion temhedral Boranes, E. L. Meutterties and W. H. Knoth, Marperature was h reduced to 90 and 5 grams f poly- 061 's 1963, and numerous Pdtents y (ethyl acrylate) as a 32% solids solution was added along these authors. with the usual coating aids including a gelatin hardener.

Among the gold compounds which will he found usfiflll, The emulsions were coated on a photographic film supthere may be mentioned hydrochloroauric acid, auric chlo- 35 port and dried in a conventional manner. Strips of the Tide, aufic bromide, Sodium and Potassium allfate, Sodium exposed emulsion elements were exposed in the above and potassium hl rg r g br m r t an i ur described sensitometer and processed in the following potassium auricyani ean potassium aurit iocyanate. manner using a 5 Step and a log exposure 425' A ig z g f z Ig It 15 g g a g fi 40 coated test strip was exposed and developed for 1 /2 Poul1 S f g0 f S 6 a 6 6 minutes at 68 F. in a developer having the following silver halide emulsion after 1t has been made, ripened composition: and washed to remove the excess soluble salts resulting from the precipitaton of the silver halides and after the Water-750 pH has been adjusted to 59.0 and preferably between 3 MCtPYIPjammOPheHOI Sulfate-'30 grams and 7.0. The preselected level of pH should be maintained b1Su1fite1-6 grams during the digestion period. After digestion, the pH is Sodlum s u1fite(anhYdruS) 45-0 grams adjusted to the desired coating pH and the conventional HYQIOQHIHOHFIZ'O grams final adjuvants are incorporated with the emulsion. Coat- Sodlul? carbna te (anhydruS)"67-5 gTams ing aids such as saponin, sodium salts of polyether sul- POPaSSIPm brm1de j1'9 gramS fonates, long chain alkyl sulfonates and sulfates, cetyl 5O Trisodium ethylene diamine tetra acetate tr1hydratebetaine, etc., can be utilized. The emulsion is then coated f onto a suitable support and dried. The conventional coat- BenZtnaZ1e0'25 g ing processes and apparatus can be used. Water to make-1'0 met The sensitomeric characteristics of the direct positive The strip was then immersed in a conventional short elements may be determined by exposing in an intensity stop for 5-10 seconds, fixed for three minutes in a conscale sensitomer, described on page 61-6, Mees, The ventional fixer, then washed and dried. Theory of the Photographic Process, Macmillan Company, In evaluation of the processed strips, the minimum blew York (1942), using a suitable step wedge and light density (D equals the lowest density above that of intenslty depending upon the inherent speed of the emulthe fixed out strip mentioned above. The maximum denssion. After exposure in the sensitometer, the strips are deity (D is the highest density above D Gamma veloped in suitable developers as shown below, immersed ('y), the slope of the characteristic -H&D curve is deterin a short-stop bath, fixed in a conventional fixing solumined in the usual manner. Sensitometric results are tron, and then washed and dried. shown in TablesIand IA.

TABLE I Mole Mole CsB H S/ HAIICI4.3H20/ Speed, mole AgNO; mole AgNOa /E Xl0- D D in Gamma 13.3)(10- 0 26.6X10-8 0 steer: s at;

13.3 10 133 59): 689 u 26. 6X10! 4. 0s 10- 364: 000 a: 49 01 05 1 22 39. 9X10 4. 96X10-4 321, 000 a. 52 0. 05 1. 0s 53. 2x10-# 4. 96X10'4 77,000 4. 30 0. 11 1. 1a 79. 8X10-! 4. 00 10 85,000 5. 16 0. 13 0. 9a

TABLE IA a Mole Mole 02BioHm/ HAI1C14.3H2OI Speed,

mole AgNO; mole AgNOz 100/E X10- Dina! Dmln Gamma 1. X10' 2 66X10 6 68X105 06BX10 0. 0. 06 13 30XlO-fl l. 0.09 1 1 20. 0X10' 3. 0. 12 1 6 26. 6X10 1. 02X10 153,000 3.63 O. 11 3 0 EXAMPLE II To an aqueous gelatin solution containing 7.95 milligrams of RhCl there was added by a twin-stream method over a 90-second period, 1 mole of AgNO and 1 mole of KBr in aqueoussolutions. The resulting emulsion was then ripened by heating with 0.73 mole of aqueous NH OH for. 10 minutes at 110 F. The emulsion was coagulated, washed and redispersed as described in Moede, U.S. 2,77 2,- 165, issued Nov. 27, 1956. The redispersed emulsion was added to an aqueous solution containing 6.1% gelatin and heated to 130 F. with the pH being adjusted to 5.5 with 0.6 M NaOH. The borane compound, (NHg B H was added as indicated in the table below followed by the ad dition of HAuCl hydrochlorauric acid as indicated.

The emulsion :was digested for minutes at 130 F. The temperature was reduced to 90 F. and 6 grams of poly(ethyl acrylate) as a' 32% solids solution was added along with the usual coating aids including a gelatin hardener. The emulsion was then coated on a photographic AgNO Upon completion of the silver halide precipitation, the composition of the emulsion was about bromide and 40% chloride. The pH was adjusted to 3.9, the emulsion was coagulated, washed and redispersed as described in Example I. The redispersed emulsion is added to an aqueous solution containing 6.1% gelatin and heated to a temperature of 130 F. The pH of the system was adjusted to 55:0.5 with 0.6 M NaOH. An aqueous solution of the cyclic borane compound CsB H S was added to portions of the emulsion as indicated in the table below together with HAuC1 as shown. The emulsions were digested at 130 F. for 40 minutes. The emulsion temperature was reduced to 90 F. and poly(ethyl acrylate) as a 32% solids solution was added along 30 with the conventional coating aids including a gelatin hardener. The emulsions were coated on a photographic film support and dried in a conventional manner.

Stirps of the films were exposed and processed as described in Example I. sensitometric data are shown in the o e I I r 4 film support and dried in a conventional manner. Strips of following table.

TABLE III Mole Mole CSBnHzzS/ HAuChJiHQO/ Speed, mole AgNOa mole AgNOa 100/E X106 D Dmin. Gamma 0 2. 46X10- 0 o 0 0 2. 4x10- 0 12, 300 3. 49 0 9.3 1o- 0 o o 0 o 9. 3X10'' 2. 46x10- 243, 000 2. 35 0. 04 1.11

the coatings were exposed and processed as described in Example I. Sensitometric data is shown below.

TABLE II a Mole Mole (NH4)2B|0H10/ HAUCMBHZOI Speed, mole AgNO; mole AgNOa 100/E X10- Dmnx. Dmln. Gamma 0 1. 02 1o- 2. x1o- 1. 02x10- 337, 000 2. 0. 00 0.80 5. 30x10- 1. 02x10- as, 500 3. so 0. 00 0.80 7, x10- 1. 02x1o- 47, 500 4. 32 0. 00 0. 73 1o. GOXIO-T 1. ozxlo- 47, 500 4. 43 0. 00 0. s0

EXAMPLE III EXAMPLE IV To an aqueous gelatin solution containing 31.8 milligrams of RhCl there was added simultaneously by the twin stream method over a period of about 200 seconds, a'salt solution containing 0.6 mole KBr and 1.3 moles of ,KCl and an aqueous solution containing 1 mole of Example I was repeated using the quantities of hydrochloroauric acid and the various borane compounds as 60 indicated in the table below. The pH of the emulsions were maintained at 7.0 during the digestion period. Ex-

posure, development and evaluation of sensitometric data was carried out as indicated in Example I.

TABLE IV Mole Boraue compound, HAuChfiEhO/ Speed 100/E mole/mole AgNOa mole AgNO; X 10- Da D CSBIHMS, 2.66X10 0 0 0 0 CsB HuS, 2.66X10 4. x10' 280,000 1. 37 0.05 [(CsH5) CH P :BuHn, 2.66X10 0 O 0. 03 [(CsH5)3CH3P gBuHu, 2.66X10- 4. 95X10 243,000 1.83 0.05 BwCgI-Im, 6.66X10' 4. 95X10' 168, 000 1.16 0. 05 Cs(CH3)4NBnH11, 6 66x1 4. 95X10' 350, 000 1.00 0.05 053135119, 2.66X10'- 4. 95x10- 102,000 4. 27 0. 05 Cs BgHu, 2.66X10L 4.95X10" 310, 000 1.02 0.05 CsBgHgCH, 2.66X10 4. 95X10- 49, 400 4.91 0. 05 CsBnHnCH, 266x10" 4. 95x10" 366, 000 74 0. 05

7 EXAMPLE v TABLE V Borane Mole/mole compound AgNOa Speed Dmax. Dmln. Gamma (NH4)2B10H10 2. 66x10 510, 000 1. 04 0. 45 CSBnHmS 2. GGXlO' plus (NHDzBwHm..- 2. 66x10 As will be seen from the above sensitometric data, the direct positive elements of this invention are extremely fast as compared to the emulsions of the prior art and much faster than when the borane compounds are used in the absence of a gold compound.

From the emulsion coated elements of this invention, good duplicates can be made by contact printing, using suitable exposing radiation. The direct positive elements may be used for reproducing continuous tone negatives, halftones, line copy, engineering drawings, etc. The direct positive elements of this invention may also find use in color photography.

The photographic elements of this invention have the advantage that they provide direct positives with extremely low minimum densities and high maximum densities. They are extremely fast and require much lower quantities of the borane and gold compounds than have been necessary heretofore in the production of chemically fogged direct positive elements. The elements of this invention may be developed in any standard developing solution such as the continuous tone developing solution set forth in Example I above or a high contrast lithographic developer using standard techniques well known in the art. Variations in the developing solution will have much the same effect as would be obtained in developing non-reversal emulsions. No pre-exposure operations or auxiliary processing procedures are necessary or desirable in using the novel elements of this invention. It is also unnecessary to utilize stain producing nonsensitizing dyes or desensitizing dyes although optical sensitizing dyes for extending the range of receptivity of actinic radiation may be incorporated in the system. Further, it is unnecessary to use high quantities of gold compounds which cause poor bleaching characteristics resulting in excess minimum densities or impure white background areas.

In place of geltain as the water-permeable colloid binder for the silver halide grains as described in the above examples, other natural or synthetic water-permeable organic colloid binding agents can be used. Such agents include water-permeable or water-soluble polyvinyl alcohol and its derivatives, e.g., partially hydrolyzed polyvinyl acetates, polyvinyl ethers, and acetals containing a large number of extra-linear CH CHOH groups; hydrolyzed interpolymers of vinyl acetate and unsaturated addition poymerizable compounds such as maleic anhydride, acrylic acid and methacrylic acid ethyl esters. Suitable colloids of the last mentioned type are disclosed in U.S. Patents 2,276,322; 2,276,323 and 2,347,811. The useful polyvinyl acetals include polyvinyl butyraldehyde acetal and polyvinyl sodium o-sulfobenzaldehyde acetal. Other useful colloid binding agents include polyvinyl butyraldehyde acetal and polyvinyl sodium o-sulfobenzaldehyde acetal. Other useful colloid binding agents include the poly-N- vinyllactams of Bolton, US. Patent 2,495,918, the hydrophilic copolymers of N-acrylamido alkyl betaines described in Shacklett, US. Pat. 2,833,050 and hydrophilic cellulose ethers and esters.

The emulsions of this invention may be coated on any suitable base including paper and transparent film support. For example, the cellulosic supports, e.g., cellulose acetate, cellulose triacetate, cellulose mixed esters, etc., may be used. Polymerized vinyl compounds, e.g., copolymers of vinyl acetate and vinyl chloride, polystyrene, and polymerized acrylates may also be mentioned. The films formed from polyesters made according to the teachings of Alles, US. Patent 2,779,684 and the patents referred to in the specification of that patent. Other suitable supports are the polyethylene terephthalate/isophthalates of British specification No. 766,290 and Canadian Patent 562,672 and those obtainable by condensing terephthalic acid and dimethyl terephthalate with propylene glycol, dimethylene glycol, tetramethylene glycol or cyclohexane- 1,4-dimethanol (hexahydro-p-xylene alcohol). The films of Bauer et al., US. 3,059,543 may also be used. The polyester films are particularly suitable because of their dimensional stability.

The emulsions are generally coated on the supports in quantities to give a coating weight of about 50-75 milligrams of silver halide per square decimeter of support surface area. Other cyclic or polyhedral boranes than those set forth above may be used. A practical limit is imposed upon the use of certain boranes due to high toxicity and possible explosive characteristics of individual compounds.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A direct-positive, water-permeable colloid-silver halide emulsion containing a boron hydride and a gold compound, in which the has a polyhedral framework containing from 6-12 boron atoms and may contain heteroskeletal atoms selected from the groups consisting of C, S, and N, wherein, the boron hydride is present in an amount of 10" to 10- mole per mole of silver, and the gold compound is present in an amount of 10- to 10- mole per mole of silver, the combined amounts of said boron hydride and gold compound being suflicient to fog said emulsion.

2. An emulsion according to claim 1 having pH 3.0-9.0.

3. An emulsion according to claim 1 containing rhodium chloride. 7

4. An emulsion according to claim 1 wherein the silver halide is a silver chlorobromide emulsion.

5. An emulsion according to claim 1 wherein the silver halide is a silver bromochloride emulsion.

6. An emulsion according to claim 1 wherein the colloid is gelatin.

7. An emulsion according to claim 1 wherein the boron hydride 1S CSBgHmS.

8. An emulsion according to claim 1 wherein the boron hydride is a polyhedral homonuclear borane of the series BgHs t0 B12H12 2.

9. An emulsion according to claim 1 wherein the boron is (NH4) B1oH1 10. An emulsion according to claim 1 wherein the gold compound is hydrochloroauric acid.

11. A photographic element comprising a support hearing a layer of an emulsion as defined in claim 1.

12. A photographic element comprising a support bearing a layer of an emulsion as defined in claim 3.

References Cited UNITED STATES PATENTS 3,411,917 11/1968 Figueras 96-64 X 3,637,392 1/1972 Bigelow 96--108 3,445,235 5/1969 Burt 9695 3,501,305 3/1970 Illingsworth 96108 NORMAN G. TORCHIN, Primary Examiner W. H. LOUIE, IR., Assistant Examiner US. Cl. X.R. 96-64 

